CLASSIFIERS OR MODIFIERS FOR

TERRESTRIAL ECOSYSTEMS

Vegetation Structure

Vegetation is the most voluminous expression of life and it can be split up in distinct structure categories, particularly forests, savannahs, prairies and sparse vegetations. Each develops under specific conditions in response to the physical ecological conditions and species interactions, while together each vegetation creates its own microclimatic conditions. As a result, tree species are usually different from shrub species, trees species in closed forest usually are at least partially different from the species making up a savannah, prairies are dominated by non-woody species, while aquatic vegetations again have very different species that make up the dominating structure. Animals strongly respond to vegetation structures, and the fauna of a forest is quite different from that of a savannah or a prairy. Vegetation being the most voluminous biotic factor in terrestrial ecosystems it can be best observed and mapped and therefore its structure is the most noticeable strongest characterizing classifier or modifier for terrestrial ecosystems distinction.

Important as local climate conditions are, the UNESCO and USNVC classification system only consider broad climatic zones like "tropical" and "temperate", with for instance, all Central American ecosystems defined as "tropical." On a worldwide scale, this obviously leads to completely different assemblages of species, but within most national maps, climate data are not commonly used as differentiating classifiers or modifiers. Indirectly, however, both systems reflect local climatic variation as different climatic conditions result in different phytological and phenological expressions of the vegetation, and thereby, those classifiers or modifiers are important climate-related classifiers or modifiers as will be shown when reviewed in the following section.

The LCCS uses growing period, moisture and temperature classes. However, the general usefulness of those direct climate data for ecosystem characterization for nationwide ecosystem differentiation must be questioned for most countries. The first classifier or modifier usually varies little on countrywide scales, and the other two, are very crude classifiers or modifiers, whose quality heavily depends on the distribution of weather stations and the quality and duration of their data series.

Whether occasionally, some explicit climatic terrestrial classifier or modifier needs to be added, must be evaluated on a case-by-case basis. Given the characteristics of other available modifiers and the often unreliable quality of available data in remote areas, the need of temperature and moisture data for the purpose of detailed biodiversity mapping, requires serious evaluation of the underlying weather data and assessment of the specific necessity for such data. E.g. in the case of the Chocó, the forests would not need to be distinguished from the western Andes flanks, as those would be distinguished already on biogeographical grounds, but within the Chocó differentiation on the basis of rainfall may need to be considered if other classifiers or modifiers could not lead to satisfactory distinction in ecosystem distinction.

The UNESCO system includes altitudinal modifiers, which are effective proxies for climatic conditions because of the strong relationship between elevation and microclimatic variation. Climatic conditions vary markedly with changes in elevation. The average temperature of a region decreases with about 0.60 C for every 100m increase in elevation (e.g. Kappelle 1996). Precipitation and humidity usually increase with elevation, although not always consistently. Sometimes rainfall may decrease again above a certain point. What is important, however, that these climatic variations with elevation create very distinct living conditions that may be mapped using digital elevation models and/or topographic map. Thus different elevation levels are very effective classifiers or modifiers that serve to differentiate ecosystems with partially different species assemblies.

Furthermore, tropical regions with humidity deficits at lower elevations, usually undergo a change in degree of seasonality as elevations increase, from deciduous or semi-deciduous to evergreen. Other conditions that change with increased elevation are: lower atmospheric density; increased direct solar radiation, particularly ultraviolet (which may be offset though, by increased cloudiness); stronger winds; and fewer solar hours because of increased cloud cover. These elevation-related conditions require distinct survival strategies of species such as increased tolerance to daily climatic seasonality with low temperatures during the night, protective layers to reduce ultraviolet exposure and reduced vegetation height due to wind suppression.

The following examples corroborate the variation of species assemblages with elevation. Since 1980 the Amsterdam and Utrecht Universities of the Netherlands and the Universidad Nacional and IGAC of Colombia carried out the Eco-Andes program (A.M. Cleef, pers. com., e.g. in Cleef 1983, Keizer et al. 2000, Cleef et al. 2003). Within this cooperative research program, systematic multi-taxa inventories along transects at different elevation levels at 7 locations in the Northern and Central Andes were carried out. Van der Hammen et al (1989) have elaborated a detailed methodology. Currently, the von Humboldt Institute (1999) carries out similar research at 6 locations, more or less evenly distributed from North to South along the eastern flank of the Colombian Andes. This and many other studies elsewhere (e.g. many documents of Kappelle, Islebe and Kappelle 1994) indicate that the flora composition varies greatly along altitudinal gradients. Wilson et al. 2001, finds distinct differentiation along different elevation levels for amphibians in Honduras. It was found, however, that bird distribution varied less distinctly along altitudinal levels than some of the other taxa, and it would make sense that endothermic species are somewhat less sensitive to elevation differentiation and would require fewer ecological distinction in elevation levels. New world monkeys are usually absent above the two lowest elevation levels (P.R. House, pers. com.) and make thus part of the species assemblage of these lowest levels.

The cooler climate conditions at higher elevation in tropical regions are very distinct from those in the temperate regions. Some of those regions have distinct seasons, such as Central America, Venezuela Peru and Bolivia, which show pronounced seasonal fluctuations in rainfall. In other areas in the Andes, like Southern Colombia and Ecuador, seasonality is bearably noticeable. A most critical distinction, however, is that many cool zones along mountain ranges in the tropics never experience freezing conditions. Many coolness tolerant species among those slopes are not likely to tolerate freezing conditions, except those at the highest elevations where cold spells or nightly frost occur. Still, those freezing conditions are different from the ones in the temperate boreal and austral climates, where cold seasons with freezing conditions set off different processes of reproduction and other elementary phases in life cycles, each genetically built into the residing species.

The UNESCO system defines the following altitudinal descriptors: Lowland, Submontane, Montane, Subalpine, and Cloud. However, it does not specify elevation ranges as those vary by geographic region or they may even depend on exposure to different prevailing climatic conditions along a mountain range. The latter was found to be the case in Central America, where the Pacific slopes are expected to abide by different elevation levels than the Atlantic slopes. It may very well be that in certain regions more or fewer elevation levels are needed. F. França (pers. com. 2006) shared his experience that around Brasilia (at about 1,000 m asl), in an environment of savannah conditions he had seen very little variation in ecosystems at different elevation levels. Under all circumstances, elevation levels need to be region defined, e.g. in the context of the Map of the Ecosystems of Central America it was defined respectively submontane between lower limit 500 – 700 and upper-limit 1,000 – 1,200m for Central America, while Prance 1989 suggests 700 – 1,200 and 1,800 – 2,400, respectively for the tropical Andes; the latter also suggests that for isolated mountains, the elevation levels are very much compressed (e.g. Trinidad and isolated volcanoes in El Salvador and Nicaragua, Meyrat et al. 2002). The elevation scale may be split up in different sizes as well, which implicitly has already been recognised by Mueller Dombois and Ellenberg (1974), where they bundle class B1a, "Drought-deciduous lowland (and submontane) forest" supposedly for being identical along a greater altitudinal range. Usually, regional differentiation in elevation levels on a continental scale is not considered important for biodiversity distinctiveness within the context of national protected areas system informatics, as they usually don’t apply within individual countries. In very large countries, however, this may need special attention from the analysers, particularly Canada, the USA, Mexico and Brazil.

Biogeographical divisions don’t form explicit parts of any of the physiognomic ecological systems. As we have seen earlier, however, biogeographical divisions may make additional distinctions of species assemblages, and a biogeographical atlas based on clear indicators cán contribute to species assemblages selection. This becomes increasingly important with the size of a country. In absence of such map and where such possibility still exists, equitative distribution of protected areas across a nation will help capture biogeographical distinctiveness on a national scale. Composition of protected areas systems by nation further increases the incorporation of biogeographically distinct species assemblages across the continents, even if we don’t know the biogeographical ranges very well.

A seasonal change in phenology is caused by partial or full shedding of foliage from the trees and/or by withering or other changes in the herbaceous layer. Seasonality is the result of seasonally unfavorable conditions or stress, which many sessile and low mobility species survive by having adopted survival mechanisms to get through the unfavorable season, such as one-year life cycles, surviving underground tissues, seasonal hiding, hibernation, and epidermal or skin desiccation protection. Many mobile species may resort to migrating to other regions or other elevation levels.

Seasonal leaf shedding in the tropics is considered a very important ecological phenomenon, as it reflects seasonal stress, usually caused by draught or flooding. Organisms living under seasonally defoliated trees are more exposed to direct solar radiation and higher temperatures. Species that can survive these conditions are clearly distinct from the ones that live permanently under conditions with sufficient moisture to remain evergreen. A note should be made that the LCCS appears to lack a category for evergreen seasonal forest, which maintain evergreen phenology in the tree stratum, but whose herbaceous stratum mostly shrivels (Meerman 2001) during the unfavorable season. For distinction of species assemblages, this category is certainly important, as species in the ground stratum that can withstand a period of draught are very distinct from those that can't. Whether or not seasonal leaf shedding generates considerable micro-climatic differences in temperate, boreal and austral climates is not so clear, as the winters cause such a dramatic change, that deciduous and evergreen forests undergo a period of seasonal dormancy. The different humus composition however from (evergreen) needle leaved and broadleaved (deciduous) forests however is very different and may create different conditions that may lead to partially distinct species assemblages, as obviously do the trees themselves.

The main categories recognised by UNESCO are broadleaved, needle-leaved, microphyllous, palmate, bambusoid, graminoid, and forbs. More than anything, these classes distinguish some of the dominant growth forms, which usually is followed by many of the accompanying species. Predominant leaf morphology may give some information about ecological conditions, particularly in the context of other data. For example, Caribbean Pine, Pinus caribea, forests in the tropics are usually more fire resistant, and indicate frequent burning. Most of the time, tropical forests are composed of a mix of trees of diverse leaf types, something which is not further distinguished in the UNESCO classes, but when leaf types can be used for differentiation, this is likely to relate to partial differentiation of species assemblages.

Duivenvoorden et al. (2001) demonstrate that drainage is one of the more determining factors in differentiating species assemblages in lowland tropical rainforests in the North-western Amazon. The UNESCO system has many drainage-based classes. For soil organisms and plants, poor drainage and flooded conditions require sophisticated mechanisms for gas exchange, escape from saturated or flooded conditions, or some form of seasonal dormancy. A huge variety of aquatic and semi-aquatic organisms are adapted to seasonally flooded or poorly drained ecosystems. With drainage being such an important ecological condition, the degree of drainage has been made explicit in the Map of the Ecosystems of Central America. In hilly and mountainous terrain, drainage was assumed good and was not mentioned for higher elevation forest ecosystems, as they all occurred in sloped mountainous terrain. In countries with distinct level mountainous plateaus, like Peru and Bolivia, such assumption may not be made, and the drainage factor must also be indicated in the classification.

In lowland forest ecosystems, an extra category was added to the UNESCO system, moderately drained - Grossman (1998) suggests an even further division - to make sure that there would be sufficient species distinction between the well-drained ecosystems in hilly terrain and the periodically waterlogged or drenched systems where species need to resort to special survival mechanisms.

Drainage is rather tricky in the sense that on a micro scale, variations occur, like mounts in a marsh and small marshy flats in forested hills. As a result, species may be added to these environments, that would not be expected on the bases of the predominant ecological conditions. For conservation purposes however, this is not problematic, as these variations merely add to the species diversity of the ecosystem under consideration.

In temperate and subpolar regions, aspect/exposure are important

With the toplayer in tact, the effect of the soil composition is relatively insignificant, as the needed elements are available and continuously recycled from the top layer. As a result, the difference between poor and rich soils are relatively little reflected in natural forests. This can be recognized in the exuberant growth of the tropical forests on often rather poor soils. Slash and burn practices also illustrate this phenomenon: After the soils are exhausted by agricultural use and left to rest, the first years they are covered with rather poor vegetation, but as time passes by, fertile elements accumulate in the top layer and eventually the vegetation matures into a better-structured forest. When applying GIS, it may seem very tempting to "overlay" an existing soil map with the physiognomic and other ecological

Overlaying a physiognomic ecological map would simply create many questionable new classes that would not or hardly reflect ecosystem differentiation. One would not know which classes would and which classes would not result in real differentiation of species assemblages and the boundaries of the polygons thus created would add additional uncertainty to the map and artificial differentiation in ecosystems.

There are a few broad soil types, however, that are known to be accompanied by specific assemblages of species and which can be valuable in an ecosystem classification. In Guatemala, the botanists (J.J. Castillo Mont, pers. com.) observed that calcareous soils or rocks provided a sufficient basis for distinguishing ecosystems, and in one case in Belize, an extraordinarily poor soil was found to have a clearly distinct assemblage or set of species. Therefore, calcareous soils are a distinguishing criterion in several classes and so do " extremely poor or sandy soils" at certain occasions. Duivenvoorden et al. (2001) also found some differentiation in species assemblages for different soils in the Western Amazon: The relatively rich sediments of volcanic origin along rivers in Ecuador and poor white sands in in various part of the Amazon region were found to have notable differentiation in species composition. Alvarez-Alonso (2005) mentions that the white sands in Alpahuayo – Mishana National Reserve near Iquitos, the white sands consisting of almost pure quartz sands are extremely poor in nutrients, while the trees represent only a few species of low stature, unique to the sands. Moreover, several endemic species of birds are restricted to the white sands forests. White sand forest have been given ample analysis for the Amazon by Prance 1989, where he elaborates "forest on white-sand soil", which, - despite different origins - have in common nutrient poor and rather well-drained soil conditions, which lead to restricted forest development and dominance of species resistant to stress conditions, as well as "local endemism".

Another soil type is peat. Often formed with Sphagnum, peat usually contains very different species assemblages that are tolerant to prolonged waterlogging and often have extremely low nutrient contents and pH values. Within peat communities, there is a distinction between those that are formed in riverine environments and periodically flooded with nutrient rich river water. Others are formed by accumulation of rainwater and almost never exposed to nutrient rich rainwater. The species compositions of those two types is very distinct.

H. van der Werff (pers. com.) advised that particularly on a very detailed scale, some special soil conditions may add certain species to an area, but that requires a level of detail – both in mapping and available soil maps or data - that usually is not available at a national scale and too detailed to be practical for ecosystem maps at a national level. From a costing point of view, systematically including soil elements in an ecosystems map would require the involvement of soil specialists, additional soil sampling and as a result, the mapping costs would almost double. In stead, the need to add certain soil elements to an ecosystems map should be assessed by experienced ecosystem mapping ecologists.

Salinity

Communities with elevated levels of salinity exist primarily in coastal environments, but not exclusively (e.g. Salar de Uyuni in Peru, Great Salt Lake in Utah, saline lakes in Mongolia, Estosha Pan in Namibia, Lake Chany in Western Siberia, etc. Plant species resistant to elevated salt conditions are relatively scarce. In the humid tropics, woody life forms dominate saline coastal environments with mangroves being the most common but not only woody species. Natural tropical open saline graminoid formations are less common, and they may still have scattered mangrove trees or bushes. Biodiversity in saline terrestrial and isolated aquatic communities is probably low anywhere in the world, but the species composition is very distinct from non-saline ecosystems.

The degree of dynamism is a key ecological characteristic with great impact on species composition and species richness. The higher the level of dynamism, the lower the number of species capable of surviving under those conditions. Usually higher dynamisms is reflected in lower vegetation cover density. Ecosystem dynamism usually is not mapped as such, but it may be intrinsically represented in certain other that is based on dynamism is a characterization of (anthropogenic) disturbance or perturbation, for which three levels have been defined for both terrestrial and aquatic ecosystems in the Ecosystems and Protected Areas Monitoring Database Manual. With regard to the degree of naturalness, it is important to make some essential observations. Many European conservationists and biologists are particularly familiar with landscapes that have developed under centuries of human land-use. Ecosystems formed under conditions without human activity are virtually absent and most nature reserves in Europe protect landscapes that depend on continuous cropping of products (forest, reed, grass, etc.) or reversing of spontaneous developments (spontaneous forestation of heath lands, marshes, etc.). Similarly, many savannahs in Africa and Asia have developed and are maintained by continuous seasonal burning, usually the result of human actions. In the USA and Canada, forests and savannahs with fire ecology regimens may be considered as partially human impacted ecosystems. Such ecosystems should be considered intact ecosystems with complete species assemblages. Whether they occur in the tropics or in temperate regions, such forests are different both structurally and in species composition from ancient and "virgin" forest ecosystems and may need to be mapped, conserved and managed as distinct ecosystems.

High ecosystem dynamism should not be confused with ecosystem stability. Natural dynamism may be a very consistent factor in an ecosystem, such as the continuously changing water table in the tidal zone. Ecosystems under a consistent regimen of dynamism may be considered stable in the context of nature conservation purposes and need to be mapped and represented in a protected area system baseline.

A seasonal change in phenology is caused by partial or full shedding of foliage from the trees and/or by withering or other changes in the herbaceous layer. Seasonality is the result of seasonally unfavorable conditions or stress, which many sessile and low mobility species survive by having adopted survival mechanisms to get through the unfavorable season, such as one-year life cycles, surviving underground tissues, seasonal hiding, hibernation, and epidermal or skin desiccation protection. Many mobile species may resort to migrating to other regions or other elevation levels.

Seasonal leaf shedding in the tropics is considered a very important ecological phenomenon, as it reflects seasonal stress, usually caused by draught or flooding. Organisms living under seasonally defoliated trees are more exposed to direct solar radiation and higher temperatures. Species that can survive these conditions are clearly distinct from the ones that live permanently under conditions with sufficient moisture to remain evergreen. A note should be made that the LCCS appears to lack a category for evergreen seasonal forest, which maintain evergreen phenology in the tree stratum, but whose herbaceous stratum mostly shrivels (Meerman 2001) during the unfavorable season. For distinction of species assemblages, this category is certainly important, as species in the ground stratum that can withstand a period of draught are very distinct from those that can't. Whether or not seasonal leaf shedding generates considerable micro-climatic differences in temperate, boreal and austral climates is not so clear, as the winters cause such a dramatic change, that deciduous and evergreen forests undergo a period of seasonal dormancy. The different humus composition however from (evergreen) needle leaved and broadleaved (deciduous) forests however is very different and may create different conditions that may lead to partially distinct species assemblages, as obviously do the trees themselves.

The main categories recognised by UNESCO are broadleaved, needle-leaved, microphyllous, palmate, bambusoid, graminoid, and forbs. More than anything, these classes distinguish some of the dominant growth forms, which usually is followed by many of the accompanying species. Predominant leaf morphology may give some information about ecological conditions, particularly in the context of other data. For example, Caribbean Pine, Pinus caribea, forests in the tropics are usually more fire resistant, and indicate frequent burning. Most of the time, tropical forests are composed of a mix of trees of diverse leaf types, something which is not further distinguished in the UNESCO classes, but when leaf types can be used for differentiation, this is likely to relate to partial differentiation of species assemblages.

Duivenvoorden et al. (2001) demonstrate that drainage is one of the more determining factors in differentiating species assemblages in lowland tropical rainforests in the North-western Amazon. The UNESCO system has many drainage-based classes. For soil organisms and plants, poor drainage and flooded conditions require sophisticated mechanisms for gas exchange, escape from saturated or flooded conditions, or some form of seasonal dormancy. A huge variety of aquatic and semi-aquatic organisms are adapted to seasonally flooded or poorly drained ecosystems. With drainage being such an important ecological condition, the degree of drainage has been made explicit in the Map of the Ecosystems of Central America. In hilly and mountainous terrain, drainage was assumed good and was not mentioned for higher elevation forest ecosystems, as they all occurred in sloped mountainous terrain. In countries with distinct level mountainous plateaus, like Peru and Bolivia, such assumption may not be made, and the drainage factor must also be indicated in the classification.

In lowland forest ecosystems, an extra category was added to the UNESCO system, moderately drained - Grossman (1998) suggests an even further division - to make sure that there would be sufficient species distinction between the well-drained ecosystems in hilly terrain and the periodically waterlogged or drenched systems where species need to resort to special survival mechanisms.

Drainage is rather tricky in the sense that on a micro scale, variations occur, like mounts in a marsh and small marshy flats in forested hills. As a result, species may be added to these environments, that would not be expected on the bases of the predominant ecological conditions. For conservation purposes however, this is not problematic, as these variations merely add to the species diversity of the ecosystem under consideration.

In temperate and subpolar regions, aspect/exposure are important modifiers, which for instance are clearly noticeable at the Pacific Coastal Mountains of British Colombia and the Rocky Mountains (G. Schuerholz, pers. com). These classifiers may be less relevant under tropical conditions, and where relevant, often their effect is restricted to rather small sites, which may fall below the level of detail of mapping; when mappable, usually all classes may be found evenly distributed among polygons.

With the toplayer in tact, the effect of the soil composition is relatively insignificant, as the needed elements are available and continuously recycled from the top layer. As a result, the difference between poor and rich soils are relatively little reflected in natural forests. This can be recognized in the exuberant growth of the tropical forests on often rather poor soils. Slash and burn practices also illustrate this phenomenon: After the soils are exhausted by agricultural use and left to rest, the first years they are covered with rather poor vegetation, but as time passes by, fertile elements accumulate in the top layer and eventually the vegetation matures into a better-structured forest. When applying GIS, it may seem very tempting to "overlay" an existing soil map with the physiognomic and other ecological modifiers already identified, and thus create a very diverse spectrum of ecological classes. We recommend against this, as many soil classes may not systematically reflect distinct assemblages of species. Moreover, most soil maps date back to the FAO maps of the nineteen seventies, and the quality of the polygons from those pre-satellite image and pre-GIS days, must be considered highly questionable. Another element of consideration against the use of soil maps, is that many of its classes are based on vegetation structure, and thereby reflect physiognomic elements, rather than systematically sampled soil composition profiles. In fact, most soil maps suffer from the same sampling bias as species collections: they are best sampled along access roads and near centres of investigation.

Overlaying a physiognomic ecological map would simply create many questionable new classes that would not or hardly reflect ecosystem differentiation. One would not know which classes would and which classes would not result in real differentiation of species assemblages and the boundaries of the polygons thus created would add additional uncertainty to the map and artificial differentiation in ecosystems.

There are a few broad soil types, however, that are known to be accompanied by specific assemblages of species and which can be valuable in an ecosystem classification. In Guatemala, the botanists (J.J. Castillo Mont, pers. com.) observed that calcareous soils or rocks provided a sufficient basis for distinguishing ecosystems, and in one case in Belize, an extraordinarily poor soil was found to have a clearly distinct assemblage or set of species. Therefore, calcareous soils are a distinguishing criterion in several classes and so do " extremely poor or sandy soils" at certain occasions. Duivenvoorden et al. (2001) also found some differentiation in species assemblages for different soils in the Western Amazon: The relatively rich sediments of volcanic origin along rivers in Ecuador and poor white sands in in various part of the Amazon region were found to have notable differentiation in species composition. Alvarez-Alonso (2005) mentions that the white sands in Alpahuayo – Mishana National Reserve near Iquitos, the white sands consisting of almost pure quartz sands are extremely poor in nutrients, while the trees represent only a few species of low stature, unique to the sands. Moreover, several endemic species of birds are restricted to the white sands forests. White sand forest have been given ample analysis for the Amazon by Prance 1989, where he elaborates "forest on white-sand soil", which, - despite different origins - have in common nutrient poor and rather well-drained soil conditions, which lead to restricted forest development and dominance of species resistant to stress conditions, as well as "local endemism".

Another soil type is peat. Often formed with Sphagnum, peat usually contains very different species assemblages that are tolerant to prolonged waterlogging and often have extremely low nutrient contents and pH values. Within peat communities, there is a distinction between those that are formed in riverine environments and periodically flooded with nutrient rich river water. Others are formed by accumulation of rainwater and almost never exposed to nutrient rich rainwater. The species compositions of those two types is very distinct.

H. van der Werff (pers. com.) advised that particularly on a very detailed scale, some special soil conditions may add certain species to an area, but that requires a level of detail – both in mapping and available soil maps or data - that usually is not available at a national scale and too detailed to be practical for ecosystem maps at a national level. From a costing point of view, systematically including soil elements in an ecosystems map would require the involvement of soil specialists, additional soil sampling and as a result, the mapping costs would almost double. In stead, the need to add certain soil elements to an ecosystems map should be assessed by experienced ecosystem mapping ecologists.

Salinity

Communities with elevated levels of salinity exist primarily in coastal environments, but not exclusively (e.g. Salar de Uyuni in Peru, Great Salt Lake in Utah, saline lakes in Mongolia, Estosha Pan in Namibia, Lake Chany in Western Siberia, etc. Plant species resistant to elevated salt conditions are relatively scarce. In the humid tropics, woody life forms dominate saline coastal environments with mangroves being the most common but not only woody species. Natural tropical open saline graminoid formations are less common, and they may still have scattered mangrove trees or bushes. Biodiversity in saline terrestrial and isolated aquatic communities is probably low anywhere in the world, but the species composition is very distinct from non-saline ecosystems.

The degree of dynamism is a key ecological characteristic with great impact on species composition and species richness. The higher the level of dynamism, the lower the number of species capable of surviving under those conditions. Usually higher dynamisms is reflected in lower vegetation cover density. Ecosystem dynamism usually is not mapped as such, but it may be intrinsically represented in certain other classifiers. It is an important parameter in an ecosystem relevé. A specific classifier or modifier that is based on dynamism is a characterization of (anthropogenic) disturbance or perturbation, for which three levels have been defined for both terrestrial and aquatic ecosystems in the Ecosystems and Protected Areas Monitoring Database Manual. With regard to the degree of naturalness, it is important to make some essential observations. Many European conservationists and biologists are particularly familiar with landscapes that have developed under centuries of human land-use. Ecosystems formed under conditions without human activity are virtually absent and most nature reserves in Europe protect landscapes that depend on continuous cropping of products (forest, reed, grass, etc.) or reversing of spontaneous developments (spontaneous forestation of heath lands, marshes, etc.). Similarly, many savannahs in Africa and Asia have developed and are maintained by continuous seasonal burning, usually the result of human actions. In the USA and Canada, forests and savannahs with fire ecology regimens may be considered as partially human impacted ecosystems. Such ecosystems should be considered intact ecosystems with complete species assemblages. Whether they occur in the tropics or in temperate regions, such forests are different both structurally and in species composition from ancient and "virgin" forest ecosystems and may need to be mapped, conserved and managed as distinct ecosystems.

High ecosystem dynamism should not be confused with ecosystem stability. Natural dynamism may be a very consistent factor in an ecosystem, such as the continuously changing water table in the tidal zone. Ecosystems under a consistent regimen of dynamism may be considered stable in the context of nature conservation purposes and need to be mapped and represented in a protected area system baseline.

Scarcely vegetated areas are found under many different conditions and their species are resilient to the extreme conditions that prevent the development of a closed vegetation cover. These ecosystems have in common that they are low in biodiversity, but the few species they harbor may include highly specialised organisms, some of which are rare, e.g. Sand Bread, (Pholisma sonorae).

The minimum required ecosystems classifiers for an ecosystems map to satisfy the needs for PA informatics should combine both terrestrial and aquatic ecosystems of the entire study area. For the terrestrial ecosystems, the modifiers should include:

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